Arc starting electrode and method of forming same



June 27, 1944. i P. L. SPENCYERQ ARC STARTING ELECTRODE 'AND METHOD OFFORMING SAME I Filed Feb. 13, 1942 lNvENTo PERCY L. SPENCER,

lsm-rme VOLTAGE CONTROL Patented June 27,

ARC STARTING ELECTRODE AND METHOD OF FORMING SAME Percy L. Spencer, WestNewton, Mass assignor toltaytheo n Manufacturing Company, Newton,

Mam. a corporation of. Delaware Application February 13, 1942, Serial1v. 431.393 13 Claims. (01. 250-215) This invention relates to ignitersfor initiating an are spot on a pool type cathode and to methods forforming such igniters.

An object of this invention is the provision of novel igniters "whichwill easily initiate an arc and are reliable and uniform in operation.

Another object of this invention is the provision of igniters havinglonger effective lives.

Wettingof-the igniting electrode material generally produces undesirableoperation. It is therefore a further object of this invention to provideigniters whose surfaces retain their nonwetting characteristics for longperiods of time and under adverse conditions.

This invention is applicable to-both the electrostatic and resistancetypes of igniters. By the electrostatic type of igniter I mean the typeof igniters comprised of a conductor covered by a thin wall ofinsulating material, which insulating material is arranged in directcontact with the cathode pool. By the resistance type of igniter I referto the type having relatively high resistance through which resistance acurrent is passed into the pool.

A feature of this invention is the provision of electrostatic igniterswhich operate on lower igniting voltages and thus without danger ofrupture of their insulating walls.

With the resistance type of igniting electrode it has been founddesirable to have the major portion of the resistance of said electrodeconfined to the area making contact with the oathode pool. Anotherfeature of this invention therefore is the provision of an ignitingelectrode having its high resistance confined to the portion thereofmaking contact with the cathode pool.

A still further object of the present invention is the provision ofmethods of forming igniting electrodes of the types described herein.

Other and further objects and advantages of this invention will becomeapparent and the foregoing obiects and features will be best understoodfrom the following description of exemplifications thereof, referencebeing had to the drawing. in which Fig. 1 is a cross-section of a tubeembodying my invention, together with a diagrammatic representation of acircuit with which said tube may be used;

Fig. 2 is a cross-section taken along line 2-2 of Fig. 1: and

Fig. 3 is a cross-sectional view similar to the one shown in Fig. 2 of amodification of my novel igniting electrode.

Referring now to the drawing, the tube illustrated comprises a sealedenvelope I containing a pool cathode 2, preferably consisting of a poolof mercury. and an anode 3. In order to provide means for initiating anare spot on the surface of the cathode pool 2, the tube is provided withan igniter 4, consisting of an electrode comprising an elongatedconductor 5 separated and insulated from the cathode pool by means of aninsulating layer 6 covering the surface of said conductor. filhisinsulating coating or layer is preferably made of glass sealed to thesurface of said conductor, preferably as described and claimed in myco-pending application Serial No. 251,069, filed January 16, 1939,wherein the insulating layer is described as having a thickness of theorder of 10 mils or less. The glass insulating layer is covered with aninsulating material, as will be more fully described hereinafter inconnection with the description 01' Figs. 2 and 3. The conductor 5 maybe of an convenient diameter, for example between 30 and 40 mils. Theigniter l is floated on the surface of the mercury pool 2 with aconsiderable length of said igniter in contact with the-surface of saidpool. Preferably, as illustrated, substantially the entire length of thecoated conductor 5 is thus in contact with. the surface of said pool.The coated conductor 5 may be of any convenient shape, as for example, astraight length.

External electrical connection is made to the conductor 5 through alead-in conductor 1 sealed through the bottom wall of the envelope I. Aflexible lead 8 connects the upper end of the lead-in conductor 1 to oneend of the conductor 5. The lead 8 is of sufficient flexibility topermit the coated electrode 5 to float freely on the surface of the pool2 and to change its position with variations in the level of said pool.As shown, the lead 8 may consist of a light coiled spring. In order toinsulate and separate the conductor 1 from the pool2, it is covered byan insulating wall 9, also preferably of glass. Since it is desired thatthe ignition occur at the floating igniting structure, the thickness ofthe glass layer 9 is preferably made substantially greater than that ofthe glass layer B. I prefer to leave the upper end of the conductorexposed as illustrated. The exposed end of the conductor I thus acts asan electrode which facilitates the transition of incipient arc spotsformed on'the surface of the pool 2 adjacent the insulating layer 6 intotrue are spots. Furthermore, as soon as such an are spot is formed, adischarge occurs between the upper end 01' the electrode 1 and the pool2 which is of relatively low voltage drop. This removes the high voltageexisting between the conductor 5, and the pool 2. .Thus .this voltageonly rises to the value necessary to initiate the are spot whereupon itis removed.

External electrical connection may be made to the cathode 2 through aleadein conductor in sealed through the lower wall of the envelope i andprojecting into the pool 2. External electrical connection may also bemade to the anode 3 through an anode lead-in conductor ii sealed throughthe upper end of the envelope I.

In tubes of the type described above, th application of a comparativelyhigh voltage between the lead-in conductors I and I will produce anincipient cathode spot at some point along the insulating layer 8 incontact with the surface of the mercury pool 2. If the anode 3 at suchtime has impressed upon it a positive voltage. said incipient are spotwill be transformed into a true arc spot which will then be maintainedby said anode.

The tube which I have described above may be utilized in a wide varietyof circuits. In Fig. 1 I have illustrated one typical circuit which maybe used. This circuit consists of an input transformer l2 having aprimary winding l3 connected to a suitable source of'alternating currentand a secondary Winding l4. One end of said secondary winding i4 isconnected to the anode lead-in conductor II. The other end of thesecondary winding i4 is connected through a suitable load l5 to thecathode lead-in conductor I0. Igniting voltage is supplied by anigniting voltage control i6 having its input I! connected to a suitablesource of alternating current. One end of the output l8 of the ignitingvoltage control I6 and tacky and these particles are embedded in theglass and adhere thereto. Minute openings. 7

depending upon the size of the diamond particles employed, are formedbetween the various particles and the layer of diamond particles thusformed is foraminous. However, by selecting sufficiently small particlesthe core may be complete ly covered.

It was found that this type of igniter operates more easily than theigniters of the prior art. In addition to having a longer operative lifeit is more reliable and uniform in starting arcing in the tube.

Referring now to Fig. 3, a resistance type of igniter is thereillustrated which may be substituted for igniter 4 in the tube andcircuit illustrated in Fig. 1. Igniter 20 is comprised of a I core 2| ofconducting material having a relativeis connected to conductor 1 and theother end thereof is connected to the cathode lead-in conductor l0.

The igniting impulses supplied by the igniting voltage control It aresynchronized with the voltage supplied by the secondary winding l4 sothat r a positive voltage is impressed on the starting anode 3 wheneveran igniting voltage impulse is supplied to the igniter.

Referring now to Fig. 2, as stated hereinbefore, the igniter I iscomprised of an elongated conductor 5 coated 'with a glass insulatinglayer 6 and having additional insulating material l9 arranged thereon.The material i9 preferably has a high dielectric constant and should becapable of withstanding the arcing occurring within the tube. It shouldbe a highly insulating material. Furthermore, it should be arranged insuch form as to accumulate the maximum electrical charge when arrangedfor operation. For this purpose Iprefer to use diamond particles, alsoknown as diamond dust. Besides being an excellent insulator and beingcapable of withstanding arcing, diamond dust has the high dielectricconstant of 16.5. The particles should be of a size small enough to passthrough mesh having 500 to 900 openings per square inch. The size of theparticles passing through mesh having 900 openings per square inch isapproximately 1 mil in diameter or less. Those passing through the 500mesh are of approximately 2 mils diameter or less.

The igniter I is preferably formed by shrinking the thin glassinsulating layer 8 on to an elongated conductor '5 of a suitablematerial such as, for example, tungsten. The glass which is heatedduring the shrinking operation is covered with the diamond particleswhile it is still soft ly high melting point, such as tungsten, on whicha sleeve 22 of conducting material having a relatively low meltingpointysuch as nickel, is arranged. Diamond particles 23 are embedded inthe nickel sleeve 22. Diamond particles capable of passing through 200,500, and 900 mesh were employed successfully in, this type of igniter.

These particles have a diameter of the order of magnitude of 5 mils. 2mils and 1 mil respectively. By selecting the size of the particlesemployed the contact resistance of the igniter can be determined. Theresistance of the igniter if desired can be made of the same order asthe resistance of the usual type of resistance igniter. The layer ofparticles thus formed is also foraminous. Igniter 20 like igniter 4 isadapted to be partly immersed in the cathode pool 2 with the layer ofdiamond particles which is embedded in. the core portion of saidigniterarranged between said core and the pool.

Igniter 20 is formed by arranging a thin nickel sleeve 22 over thetungsten core 2|. Diamond dust particles of the desired size are packedin a crucible and the tungsten core together with the nickel sleevearranged thereon is inserted into the crucible with the diamond dustparti- 7 cles tightly packed thereabout. The crucible is then heateduntil the nickel sleeve is fused, the nickel sleeve thereby wetting thetungsten and upon cooling adhering thereto. When the nickel sleeve is insoftened condition the dust particles are embedded therein and adherethereto.

The following is my present understanding of the theory of operation ofthis resistance type of igniter. The mercury of the pool cathodeprojects sufliciently into the openings formed between the particles tomake at least a point contact with the underlying core. Due to the smallsize of such openings the area of such contact is small and therebypresents a path of relatively high resistance to the current flow. Theresult is therefore an igniter which has operating characteristicsanalogous to those of the usual type of resistance igniter.

It was found that resistance igniters of the type hereinbefore describedpossess a longer operative life and are more uniform and reliable inoperation. Because of the concentration of the high resistance of saidigniters at the surface of the electrode, such igniters are moreeflicient in operation.

Figs. 2 and 3 are schematic and are distorted in order to more clearlyshow appl cant's structure. They are not intended to show the dimensionsof the various parts relative to each other.

While I have shown and described specific embodiments of my invention itis apparent that various modifications may be made without departingfrom the teachings thereof. For example, the type of core employed mightbe changed, and the form of the igniter or the glass insulating layermight be altered without departing from the teachings of this invention.Modifications in the steps of the methods of forming these igniters willreadily suggest themselves. It is accordingly desired that the appendedclaims be given a broad interpretation commensurate with the scope ofthe invention within the art.

' What is claimed is: v

1. An igniter for starting an are spot on a cathode pool comprising acore and a layer of discrete particles of insulating material arrangedon said core between said core and the cathode pool and formingrestricted interstices therebetween.

2. An igniter for starting an arcspot on a cathode pool comprising acore and a layer of discrete particles of insulating material having ahigh dielectric constant arranged on said core between said core and thecathode pool and forming restricted interstices therebetween.

3. An igniter for starting an are spot on a cathode. pool comprising acore and a layer of discrete particles of insulating material having ahigh dielectric constant and capable of with- '7. An igniter forstarting an are spot on a cathode pool comprising a core and a layer ofI discrete particles of insulating material having a standing arcingarranged on said core and forming restricted interstices therebetween.

4. An igniter for starting an are spot on a cathode pool comprising acore and a diamond layer arranged on said core.

5. An igniter for starting an are spot on a cathode pool comprising acore and a foraminous layer of discrete particles of insulating materialarranged on said core between said core and the cathode pool. 1

6. An igniter for starting an are spot on cathode pool comprising a coreand a foraminous diamond layer arranged on said core between said coreand the cathode pool.

diameter of an order of magnitude of 5 mils or less arranged on saidcore between said core and the cathode pool.

8. An igniter for starting an arc spot on a cathode pool comprising acore and a diamond layer, said last-mentioned layer being comprised ofparticles having a diameter of an order of magnitude of 5 mils or lessarranged on said core between said core and the cathode pool.

9. An igniter for starting an arc spot'on a cathode pool comprising acore and a layer of discrete particles'of insulating material embeddedin said core and forming restricted interstices therebetween.

10. An igniter for starting an are spot on a cathode pool comprising aconducting core, an insulating layer arranged on said core, and a layerof particles oi insulating material arranged on said insulating layerbetween said core and the cathode pool.

11. An igniter for starting an are spot on a. 1 cathode pool comprisinga conducting core, a

glass insulating layer arranged on said core, and a layer of particlesof insulating-material arranged on said insulating layer.

12. An igniter "for starting an arc spot orra cathode pool comprising aconducting core having a high melting point, a layeroi' conductingmaterial having a relatively lower melting point arranged thereon, and alayer of particles of insulating material arranged on said conductinglayer.

13. An igniter for starting an are spot on a cathode pool comprising acore,.an insulating layer arranged on said core, and a diamond layerarranged on said conducting layer.

PERCY L. spmzcan.

